(Prefatory Note: The following is intended as a detailed explanation of the justification for the present invention. It is believed that this information will assist the skilled reader in appreciating the various aspects, features and applications of the invention. While this background section makes reference to, and draws support from, various prior-art sources (such as published articles), significant portions of this section present the inventor's own analysis and findings which, though based upon the prior art, is not prior art itself. Accordingly, no assumption should be made that non-published information discussed in this background section constitutes, by admission or otherwise, prior art to the present invention.)
Blood flow is a specific indicator of medical condition and cardiovascular health, however, its measurement impracticality is impeding focus on important problems:                inadequate warning of abnormal blood flow and volumes in hospital care;        ineffective warning of conditions that cause heart attacks and strokes;        high mortalities of septic shock and drug problems;        ineffective assessment and costly management of congestive heart failure;        brain impairment with surgery of patients with cardiovascular disease; and        ineffective disease management due to inaccuracy and limited relevance of BP.        
Hospital pulse oximeter medical devices are practical for measuring relative hemoglobin oxygen content in the blood, however, the impracticality of measuring blood flow and its companions, perfusion and cardiovascular disease, has caused these physiologic parameters to be neglected for a long time. Invasive monitoring is costly and has inherent risks, and noninvasive flow monitoring has been unreliable and impractical: instead, blood pressure, pulse oximeter and ECG monitoring is used, which inadequately specify patient condition. ECG trace monitoring also lacks practicality and hemodynamic significance. Thus, clinicians are dependent on blood pressure (the simple blood pressure cuff is used professionally over 12 billion times yearly) and pulse oximeters to determine patient condition and treatment needs.
Physicians rely on blood pressure as the principal indication of blood flow and cardio-vascular disease, but this is often misleading, especially with abnormal flows. The relationship between flow and pressure is misunderstood and unpredictable. Even when measured accurately, BP yields little information about its companion blood flow, the carrier of nutrients and waste products. Nor is blood pressure a specific measure of cardiovascular disease, a principal cause of impaired blood flow and perfusion.
Physiologic sustainment depends on “perfusion”, i.e., the blood flow transport of oxygen and other materials through conduit arteries, arterioles and capillaries to tissue. Pulse oximeters are mistakenly used as an indicator of perfusion while being used to monitor blood oxygen; this is because these devices give no indication of reduced blood flow transport until flow ceases altogether. Moreover, pulse oximeter oxygen content measurements can be many minutes latent without this being recognized by the anesthesiologist.
The above misleading measurement propensities may be part of why an estimated 25% of the population are said to be untreated or treated inappropriately. Exemplifying effects of this in hospital care, authorities “have produced very convincing evidence that the so-called vital signs of every day medical care have little to do with the survival of the critically ill patient.” See C. Bryan-Brown, Blood Flow to Organs: parameters for function and survival in critical illness, Critical Care Med. 16:170 (1988).
Additional observations about monitoring of blood flow are:    1. Blood flow is pulsatile, moving forward only briefly during each heart beat; accurate measurement requires computations based on flow waveforms, which is not done with approximative heart catheterization and other methods that are used today in hospitals.    2. Blood flow is abnormally low, by as much as 60%, in those with cardiovascular disease. See M. E. Safar, Pulsed doppler: diameter, flow velocity and volumic flow of brachial artery in sustained essential hypertension. Circulation 63:2 393–400 (1981). Also see T. B. Levine, Regional blood flow supply and demand in heart failure. Am Heart J 120:1547 (1990). Conversely, elevated flows are usually associated with blood infections, anemia, various hormonal imbalances, anxiety and any physical activity. See A. C. Guyton's Textbook of Medical Physiology, FIG. 23–5, W. B. Saunders Co. (7th ed. 1986).    3. The body's total blood flow (cardiac output) varies greatly to meet physiologic needs; the variable portion of the cardiac output is the approximate 70% of high resistance flow to skin, skeletal muscle and organs other than the heart and brain; high resistance flow is controlled by the sympathetic nervous system and arteriole arteries with strong contractible vessel walls. Forearm blood flow of the brachial artery is representative of this blood flow “safety reserve” that serves to protect the brain and heart from disruptions of supply. Limb blood flow monitoring, therefore, can be a valuable analytical indication of cardiac output because it is a more obvious and earlier warning of physiologic transitions than cardiac output, which is a weighted average of both high and low resistance blood flows.    4. Although low blood flow and blood pressures generally change together, pressure and flow do not correspond at relatively normal and higher blood pressures as is commonly believed. Blood flow decreases at higher blood pressures, and the amount and rate of diminution varies among individuals. Flow varies unpredictably because the body's auto-regulation processes strive to maintain blood pressure constant and because of cardiovascular disease. Large unrecognized flow abnormalities can go unnoticed for long periods of time when blood pressure monitoring is relied upon.    5. Blood pressure also hides vital regional flow variations within the circulatory system. When cardiac output is reduced, blood flow is usually maintained to the heart and brain, while flow to other less critical regions and organs is total shutdown, which would be when flow to the brain becomes compromised. This redistribution normally occurs in part by auto regulated constriction of the wall muscle of thousands of end-arteries (arterioles). Some degree of predictability might apply to the hemodynamic effects of such vasoactivity if it were not for cardiovascular disease. However, thickened arteriole walls causes significant static impairment of the flow safety reserve, a high risk of adverse consequences of hospital patients with cardiovascular disease.    6. Anesthesiologists and critical care providers use pulse oximeters to measure the oxygen content in peripheral blood hemoglobin (the “O2SAT”), usually in a patient finger. Although an indication of respiration or ventilator function, the O2SAT does not reflect the blood oxygen transport, or “perfusion”. Perfusion monitoring involves measuring pulse oximeter O2SAT and blood flow most preferably in the main artery of a left arm, whereby a beat-by-beat blood flow value can be multiplied by the corresponding O2SAT oxygen content to determine the perfusion value or index for display on the monitor screen.    7. Along with being an erroneous indicator of blood flow, the pulse oximeter O2SAT values can be misleading indicators of respiratory function during and after periods of blood flow change, which is when measurement reliability is often most critical. Thus, anesthesiologists may be misled into erroneously (i) believing blood flow is normal when it is greatly reduced (such as just prior to cardiogenic shock) to being as little as 5% of normal, (ii) believing a distressed patient with a respiratory or ventilator problem is normal for minutes before the pulse oximeter discloses the problem, and (iii) treating a patient for a respiratory or ventilator problem that no longer exists.    8. Blood flow reveals critical conditions significantly earlier and more specifically than does blood pressure. In emergency rooms, patients can be in cardiogenic shock with peripheral blood flow shutdown for a prolonged period before blood pressure changes significantly whereby it often “crashes” to first reveal the condition. In critical care, it is believed that practical flow monitoring can provide early warning of drug interactions and dosage errors that kill over 44,000 hospital patents, and septic shock (e.g. systemic inflammatory response syndrome) that afflicts 751,000 hospital patients annually and kills 215,000. See studies in Critical Care Medicine magazine report of hospital discharges as reported in Wall Street Journal (Sep. 11, 2001), E. Haber, Harvard Medical School, Center for Prevention of Cardiovascular Disease, as reported in USA Today (Sep. 25, 1996); D. Bates, Harvard Medical School “Study Finds Drug-Reaction Toll Is High” (Associated Press Apr. 14, 1998); and W. Richardson,'s W. K. Kellogg Foundation Institute of Medicine committee report (Dec. 10, 1999). In surgery, when practical blood flow monitoring is available, the hemodynamic cardiovascular conditions that cause neuropsychiatric brain dysfunction (discussed below) and heart attacks may be identified for preventive intervention.    9. In addition to not providing an indication of blood flow changes, present non invasive blood pressure devices, by not taking into account blood flow variations, often give inaccurate or delayed blood pressure readings, which occur most commonly for the critically ill and patients with cardiovascular disease. Blood pressure inaccuracy and the lack of continuous surveillance are acknowledged hospital safety and health care issues.    10. With cardiovascular adversity probably being the greatest risk of hospital care, physicians need an effective means of warning of disease and drug interactive toxicity effects that cause heart attacks, strokes and neuropsychiatric dysfunction morbidity. See G. W. Roach, et al. Adverse cerebral outcomes after coronary by-pass surgery. NEJMed v335 no25 (1997). As part of this, prior to and during surgery, anesthesiologists need a reliable way, without trial and error, to select and gauge effects of powerful vasoactive agents. Along with blood flow, the heart loads (resistance) and work are important. For example, if the source of low blood flow is the heart, avastly different drug regimen is used than if flow is decreasing because of high peripheral arterial resistance. The simultaneous determination of central and peripheral blood flow and heart loads is needed for many patients.
Beyond the needs of hospital monitoring, the literature is replete with indications of need for better measurement and knowledge of the cause and effects of cardiovascular disease. It is widely held that early and more specific disease measurement of at-risk cardiovascular disease patients can reduce heart attacks, strokes and congestive heart failure rates. Hemodynamic science indicates that hemodynamic principles need be applied to achieve reliable non-invasive blood pressure accuracy. Hemodynamic science also teaches that, even if measured accurately, blood pressure can not be a reliable indication of cardiovascular disease. High blood pressure readings cannot reveal if the effect is temporary, such as being caused by a drug reaction, or is chronic and an effect of cardiovascular disease or other origin. Moreover, if it is the effect of cardiovascular disease, elevated blood pressure can not disclose: (i) the stage of the disease; (ii) whether it might be worsened by a drug therapy; (iii) how rapidly the condition is worsening; and (iv) the resulting increased likelihood of heart attack and stroke. The significance of these limitations is that present measurement methods are effectively contributing to reduced life span. Prevention of the disease, heart attacks and strokes for approximately 80 million Americans is needed, including for 35% of those with cardiovascular disease that will experience sudden death without prior diagnosis, largely because of understated and inconsistent BP measurements. A broader patient population needs to be screened, diagnosed and monitored in hospitals using more specific information, and at an earlier phase in the disease progression, for more effective preventive care. This raises vital issues:                Diagnosis and management of cardiovascular disease is based primarily on risk factor information that is inexact and subjective;        The reduced blood flows of cardiovascular disease can distort non invasive blood pressure measurement accuracy;        Blood pressure is a fluidic measure that tells little about effects on the heart and arteries. To illustrate, at a high blood pressure, thicker artery walls are damaged less than thin artery walls when other aspects are unchanged; and        Biophysics, based on Newton's second law, indicates that blood flow anomalies must be a major unrecognized determinant of cardiovascular disease.        
Unlike most other diseases, biochemical factors may not to be the principal initiator of cardiovascular disease. Historically, research has been focused mostly on cholesterol, homocysteine, nitric oxide and artery wall relaxation. However, these appear to be secondary effects of a more basic underlying biophysical cause. See G. L Duff, Experimental cholesterol arteriosclerosis and its relationship to human arteriosclerosis. Arch. Path. 20:81–123; 259–304 (1935). As evidence of current thinking, Dr. Paul Ridker, Harvard Medical School, is credited for discovering an inflamed coronary artery phenomena and a related sudden “popcorn” closure, the precipitating event of 70% of heart attacks. Although the cause of artery inflammation is not known, Ridker indicates it is “characterized by a decades-long cycle of irritation, injury, healing and re-injury to the inside of the blood vessels.” This source also states “researchers wonder if more benefit might be gained by investigating causes of the arterial injury”. R. Winslow, Heart-disease Sleuths Identify Prime Suspect: Inflammation of Artery. Wall Street Journal Oct. 7, 1999.
Hemodynamics researchers have yet to measure physical phenomena that science would assert to be an acceptable biophysic cause of hypertension, cardiovascular disease and its mortality. Specifically, in material science, excessive higher frequency stresses (internal forces of materials that exceed stress limits) are known to produce tiny structural fractures that can invite intrusion by extrinsic elements. This concept must apply to blood flow conditions that alter and cause deterioration of the principal cardiovascular vessels (left heart and arteries). By applying elasticity stress measurement relationships, physiologic simulations conducted by the inventor reveal that higher frequency artery elasticity moduli can easily exceed the limit of cardiovascular elastin-smooth muscle wall structure. This limit, according to measurements of hemodynamic researchers that assessed the effects of contractility and frequency, is approximately 13×106 dynes/cm2. See D. A. McDonald's Blood Flow in Arteries, Arnold Press (1960), pages 244, 268 and 279. The simulated high or erratic heart rates, as well as waveforms that are indicative of vasoconstriction (e.g., caused by nicotine) and cardiovascular disease, produces higher frequency elastic stiffnesses that exceed the limit by many times.
With 41% of U.S. mortality being related to cardiovascular disease (as compared to 23% being cancer-related), scientifically acceptable measurement and analytical relevance is needed for understanding and controlling the cause and progression of the disease. Thus, biophysic pulsatile cardiovascular stress is a measurement that is needed to improve the specificity of blood pressure measurement, and may become valuable for physicians to specify the most effective pharmacologic treatment regimen for patients and for determining when patients should be referred for costly diagnostic tests. Cardiovascular stress measurement specificity in disease management can also confirm the nature of the commencement of hypertension and cardiovascular disease, which is hypothesized to occur irreversibly in infancy. Simulations suggest that excessive stresses, which are produced by underdeveloped or slower developing infant hearts, may be a principal catalyst of cardiovascular disease. Specifically, a fast heart beat (e.g., 110–140 BPM at birth), which is needed to supply the body's oxygen, produces significant higher-frequency pulsatile stresses, even at lower blood pressure. Relatively smaller, or slowly developing, infant hearts would need to continue beating at a fast rate for a larger number of months or years before the heart's growth catches-up to fulfill the body's circulatory needs at a normal lower heart rate. It is believed that the extra work of prolonged increased pulsatile wall stress of end-arteries (the arterioles and pre-capillary sphincter vessels) cause excessive developmental thickening of the end artery muscular walls. Such thickening results in smaller, statically constricted lumen, like thicker donuts with smaller holes.
The mathematics of biophysic stresses that are presented herein show that, once initiated, unfavorable stresses and impaired cardiovascular function are likely to progressively worsen throughout life. This is consistent with the growing severity of the disease phases: artery thickening and damage to artery linings; cholesterol lipid infiltration; arteriosclerosis; calcification recomposition; coronary artery inflammation; and end-stage plaque fragmentation and “popcorn” rupture that produce strokes and heart attacks. The nonlinear elastic stress relationship suggests that the late-stage disease phase is likely to accelerate greatly and extend within the circulation in a matter of a relatively few years of life. Clinical evidence of this is that later-stage heart disease stresses would be and apparently are directly related to reduced cardiac stroke volumes of left ventricular hypertrophy or “LVH”, which has been strongly linked to both heart attacks and high rates of post-surgery neuropsychiatric brain dysfunction morbidity, e.g., up to 70% of bypass procedures and 53% of general surgery patients, of which over half are permanent impairments. See S. Newman, Incidence and nature of neuropsychological morbidity following cardiac surgery. Perfusion 4:93–100 (1989). Also see T Monk, MD, Cerebral O2 Decrease Linked to Post-Op Cognitive Dysfunction, Anesthesiology News (April 2001). Also see M. Newman, MD, Longitudinal Assessment of Neurocognitive Function After Coronary-Artery Bypass Surgery. NE J Medicine 344:6 (2001). This is probably related to thickened brain arterioles; although blood flow is normally constant in the brain, research has shown that brain flow decreases at two-thirds the rate of the large cardiac output reductions that occur in ambulatory individuals with LVH congestive heart failure. Reduced blood flow, and its related excessive stresses, may also explain the apparent relationship between high blood pressure and impaired memory and intellectual function later in life. See L. J. Launer, et al. The association between midlife BP and late-life cognitive function. JAMA.274:1846–51 (1995). Thus, the measurement of patient biophysical cardiovascular stress, relation to the late-stage acceleration phase, can be an important part of cardiovascular disease management.
Biophysic cardiovascular stress can also be the central aspect of several types of drug reactions. Specifically, drugs that alter the contractility of the heart and arterioles or cardiac rhythm in patients can accelerate cardiovascular stresses, the disease progression and its adverse incidents. These include psychotropic (e.g., Ritalin and Prozac), diet (Pondimin) and blood pressure lowering (Poisicor, Isradipine and Cardula) drugs. For example, in a major study, Isradipine nearly doubled heart attacks and strokes. See Borhani et al. “Results of Multicenter Isradipine Diuretic Atherosclerosis (MIDAS) Study” JAMA 276:10 (1996); Associated Press release “i Roche pulls Posicor from world market” (Jun. 9, 1998); and Dow Jones Newswire “Pfizer Faces Lawsuit over alleged risks of hypertension drug” (May 31, 2000). Moreover, the costs of this are great, as evidenced by the $12 billion that had to be set aside for claims related to rapid and extensive heart valve disease caused by the Fen-Phen diet pill. See American Home Products press release; WSJournal (Jan. 25, 2001).
Another matter is the need for measurement practicality for more effective preventive care for a broad patient population such as is now being monitored by blood pressure and pulse oximeter devices. Cardiovascular measurement is limited by patient risk and costs of measurement; excluding imaging systems, the measurement of blood flow and continuous blood pressure monitoring has been invasive; requiring the use of tubing in the heart, esophageal channel and/or vital arteries; moreover this is limited to a short time period because of infection spread, adverse patient reactions, and artery inadequacy, as well as clotting and micro bubbles that cause significant inaccuracy. Furthermore, noninvasive blood pressure devices are also inefficient and costly; they do not provide continuous surveillance; they are not tolerated by patients because repetitive cuff pressurizations causes trauma and circulatory anomalies, they use flawed empirical methods that causes significant inaccuracy when artery elasticity and blood flow are abnormal, and cuffs are a major source of cross contamination of staphylococci infection and other sepsis in hospitals. To overcome these measurement obstacles, an easily and lightly applied noninvasive patient sensor is needed that can provide (a) comfort; (b) continuous beat-by-beat surveillance; (c) greater measurement reliability; and (d) measure and monitor blood flow and other vital parameters; and (e) to optionally provide for reducing hospital cross-contamination and sepsis by requiring care providers to dispose of patient sensors after a programmed time of use and to use sensors on only one patient.
Summarizing, blood pressure, even when measured accurately, is an ineffective indication of hospital patient safety or disease condition. Flow and perfusion monitoring should be a standard of surgery and critical care, especially for patients with cardiovascular disease. Biophysical stress and cardiac hemodynamic profiles would be a more specific characterization of coronary artery inflammation, propensity for heart attacks and for preventing and managing the progression of cardiovascular disease.
A vast array of devices/systems/methods for characterizing and/or monitoring cardiovascular parameters appear in the prior art. Nevertheless, none of these provides a practical and economical solution to the monitoring needs of the medical community. For example, U.S. Pat. No. 5,876,347, METHOD FOR VASCULAR IMPEDANCE MEASUREMENT, to Chesey et al. purports to compute stroke volume as a linear function of ejection time, body surface area, age and heart rate. See '347 patent, column 5, lines 12–20. However, this linear model is, at best, a crude approximation of reality—and the '347 inventors essentially admit as much. See '347 patent, column 5, lines 27–30 (claiming an “accuracy” of +/−25% in 90% of patients).
U.S. Pat. No. 6,117,087, METHOD AND APPARATUS FOR NONINVASIVE ASSESSMENT OF A SUBJECT'S CARDIOVASCULAR SYSTEM, to Kamm et al. describes a technique for estimating cardiovascular model parameters by comparing model-predicted results with measured data.
U.S. Pat. No. 5,730,138, METHOD AND APPARATUS FOR DIAGNOSING AND MONITORING THE CIRCULATION OF BLOOD, to Wei-Kung discloses a system which computes the spectral frequency components of real-time BP waveforms and analyzes the various spectral components, using principles of Chinese medicine, to ascertain the health of various organs. See, e.g., '138 patent, column 3, line 33–34 (“[t]he harmonic for the liver is known to be the first harmonic of the heartbeat”) and lines 37–38 (“[t]he harmonic for the kidney is known to be the second harmonic of the heartbeat”). The '138 patent does not teach or suggest the computation of any physically meaningful cardiovascular parameters; nor does it teach any means or method for performing such computation.
U.S. Pat. No. 5,103,828, SYSTEM FOR THERAPEUTIC MANAGEMENT OF HEMODYNAMIC STATE OF PATIENT, to Bohumir suggests that stroke volume can be calculated as a multiplicative function of equivalent thoracic length (cubed), ventricular ejection time and peak ejection velocity, divided by thoracic fluid bioimpedance, with equivalent thoracic length derived from the patient's height and weight. See '828 patent, column 15. Here, too, the model is not based on physical reality. Indeed, the '828 patent even states: “The only absolutely accurate blood flow measurement method . . . is a calibrated cylinder to collect blood and a stopwatch.” ('828 patent, column 4, lines 54–59.)
U.S. Pat. No. 4,205,688, METHOD AND APPARATUS FOR DEVELOPING AND MEASURING PULSED BLOOD FLOW, to Hauser et al. provides a combined electromagnetic/occlusive-cuff apparatus which purports to measure arterial blood flow in a limb. The '688 method/apparatus makes no attempt to model, estimate or quantify the physical parameters that control blood flow (e.g., radius, elasticity, etc.) in arteries.
U.S. Pat. No. 4,240,294, FLOW METER, to Grände et al. discloses an in-line type of flow meter adapted for use in kidney dialysis and heart/lung machines. Such device is neither useful for, nor adaptable to, non invasive applications.
U.S. Pat. No. 5,241,963, METHOD FOR DETECTING THE ONSET AND RELATIVE DEGREE OF ATHEROSCLEROSIS IN HUMANS, to Shankar provides a non invasive method/apparatus for determining peak “arterial compliance,” defined as the ratio of arterial volume change, ΔV, to change of pulse pressure (i.e., systolic less diastolic), ΔP. The '963 patent does not suggest any use of such “arterial compliance” for continuous monitoring of blood flow, or show any scientific relevance or relationship of this empirical index to scientific measures of artery elasticity or flow resistance.
U.S. Pat. No. 5,755,229, PULSE WAVE ANALYSIS DEVICE, to Amano et al. discloses a method/apparatus for using fast Fourier transform (“FFT”) analysis of signals from a finger-mounted pressure cuff. Like the previously-cited '138 patent, the '229 patent does not measure any physically meaningful cardiovascular parameters. (See, e.g., '229 patent, column 1, lines 24–29, where “According to this form of pulse diagnosis, a disease can be diagnosed accurately only when the practicing ‘sage’ feels the patient's pulse. It might be extremely useful if the same diagnosis could be performed by a machine.”).
U.S. Pat. No. 4,651,747, WAVEFORM INFORMATION OBTAINING TECHNIQUES ASSOCIATED WITH AN INDIVIDUAL'S BLOOD PRESSURE; U.S. Pat. No. 4,712,563, METHOD OF AND APPARATUS FOR DETERMINING THE DIASTOLIC AND SYSTOLIC BLOOD PRESSURE OF A PATIENT; U.S. Pat. Nos. 4,664,126, 4,699,151, 4,697,596 and 4,699,152, TECHNIQUES FOR OBTAINING INFORMATION ASSOCIATED WITH AN INDIVIDUAL'S BLOOD PRESSURE INCLUDING SPECIFICALLY A STAT MODE TECHNIQUE; U.S. Pat. No. 4,564,020, METHOD AND APPARATUS FOR OBTAINING AN INDIVIDUAL'S SYSTOLIC BLOOD PRESSURE; and U.S. Pat. No. 4,154,238, APPARATUS AND PROCESS USING SECOND DERIVATIVE OF OSCILLOMETRIC WAVEFORM FOR PRODUCING SPHYGMOMETRIC INFORMATION, all to Link, disclose various methods/apparatus for using pressure cuff waveform data to obtain and/or track systolic and diastolic blood pressure. None of these Link patents teach or suggest any method for computing or estimating blood flow, even though blood flow is a principal determinant of the noninvasive physiologic measures that are sensed for computing estimates of blood pressure in present blood pressure measurement devices.
U.S. Pat. No. 5,301,675, APPARATUS FOR MEASURING BLOOD FLOW VELOCITY AND BLOOD FLOW VOLUME IN AORTAS, to Tomita et al. discloses a technique, using multiple cuffs, to estimate the propagation velocity of the pulsatile wavefront along the brachial artery and to use this velocity information to estimate flow rate in the aorta. The '675 technique does not attempt to model or compute the physical parameters that actually govern arterial blood flow, but instead, relies on an assumption that: “when a cuff is put around an upper arm and a pressure thereof . . . is retained at systolic pressure SP, a velocity at which a pulse wave clears the pressing cuff is approximate to a blood flow velocity VH in the high pressure period . . . of the aorta.” ('675 patent, col. 10, lines 21–26.) U.S. Pat. No. 5,423,324, APPARATUS FOR DETECTING AND DISPLAYING BLOOD CIRCULATORY INFORMATION, to Tomita teaches use of low-pressure monitoring cuff, secured around the upper arm, to provide an approximate real-time aortic pressure waveform.
U.S. Pat. No. 5,289,823, NONINVASIVE AORTIC BLOOD FLOW SENSOR AND METHOD FOR NONINVASIVELY MEASURING AORTIC BLOOD FLOW, to Eckerle, teaches an approach for estimating aortic blood flow by modeling a “2-cm section of the aorta, together with the two subclavian arteries,” as a “capillary- (or orifice-) type flowmeter.” ('823 patent, col. 2, lines 26–29.) Using this “flowmeter” analogy, blood pressure signals from arteries in the left and right arms are combined to provide an estimate of aortic flow. The '675 patent does not teach or suggest any method for measuring flow at the site(s) where the actual blood pressure signal is being measured.
U.S. Pat. No. 3,920,004, DEVICE AND METHOD FOR NONINVASIVE MEASUREMENT OF BLOOD PRESSURE, RESISTANCE INERTANCE, COMPLIANCE, IMPEDANCE, BLOOD FLOW RATE, KINETIC ENERGY, FLOW VELOCITY AND PULSE VELOCITY OF A SEGMENT IN MAN, to Nakayama discloses a system using distinct pressure and volume sensors, both positioned along the same artery. The '004 patent does not teach or suggest any method for computing a real-time flow waveform, nor any frequency domain cardiovascular or hemodynamic parameters.
U.S. Pat. No. 4,243,648, METHOD AND APPARATUS FOR MEASURING BLOOD PRESSURE AND PULSE RATE, to Trimmer et al. discloses a device utilizing two spaced-apart arterial pressure transducers to capture various aspects (e.g., rise time, transit time) of the real-time pulse pressure signals, which aspects are used to compute systolic/diastolic pressure and pulse rate.
U.S. Pat. No. 3,095,872, BLOOD PRESSURE MEASUREMENT, to Tolles teaches a method for measuring blood pressure by impressing a substantially-higher-than-heart rate signal upon an artery and detecting phase changes in said signal as it travels along the artery.
U.S. Pat. No. 3,104,661, SYSTEM FOR CONTINUOUS BLOOD PRESSURE DETERMINATION, to Halpern discloses a blood pressure measurement device having an inflatable cuff and separate pressure transducer.
U.S. Pat. No. 4,649,928, NOISE-IMMUNE BLOOD PRESSURE MEASUREMENT TECHNIQUE AND SYSTEM, to Samaras et al. teaches a device having separate occlusion and sensing cuffs, and a method for detecting blood pressure in noisy environments without having to detect individual heart pulses.
U.S. Pat. No. 4,858,616, BLOOD PRESSURE MEASUREMENT SYSTEM FOR FILTERING LOW-FREQUENCY, HIGH-AMPLITUDE NOISE, to Samaras et al. provides an apparatus similar to the '928 Samaras et al. patent, but with an additional capability to “recognize slow, large noise signals” created by patient movement and “filter out these slow, large noise signals.” ('616 patent, col. 2, lines 43–44 and 46–47.)
U.S. Pat. No. 5,152,296, DUAL-FINGER VITAL SIGNS MONITOR to Simons discloses a device with “a pair of finger cuffs that each include an, electrocardiograph electrode, a first radiation source and detector pair for blood pressure measurement, and a second radiation source and detector pair for blood oxygenation measurement.” ('296 patent, col. 2, lines 10–14.)
U.S. Pat. No. 5,050,613, METHOD AND APPARATUS FOR VASCULAR TESTING, to Newman et al. discloses a system which includes a plurality of pressure transducer(s) and/or cuff(s), positioned at various sites (e.g., upper arm, thigh, ankle) on the patient. Signals from the various transducer(s) are compared/evaluated to detect cardiovascular abnormalities, such as arterial blockages.
U.S. Pat. No. 4,729,382, METHOD AND APPARATUS FOR UTOMATICALLY DETERMINING PULSE RATE AND DIASTOLIC AND SYSTOLIC BLOOD RESSURE, to Schaffer et al. discloses an automatic blood pressure measuring device that includes inflatable occlusion and sensing bladders, each surrounded by a rigid tube.
U.S. Pat. No. 5,099,852, METHOD FOR DETERMINING THE ARTERIAL BLOOD PRESSURE IN A NONINVASIVE MANNER, to Meister et al. teaches a method for using two, spaced-apart ultrasonic transducers to monitor arterial diameter at two locations along an artery and, from these measurements, compute propagation velocity, pulse rate, compliance and pressures. U.S. Pat. No. 5,152,297, METHOD AND APPARATUS FOR ESTABLISHING THE PRESSURE-DIAMETER RELATIONSHIP OF AN ARTERY BY NONINVASIVE MEASURES, to Meister et al. utilizes a similar approach.
U.S. Pat. No.5,101,828, METHODS AND APPARATUS FOR NONINVASIVE MONITORING OF DYNAMIC CARDIAC PERFORMANCE, to Welkowitz et al. discloses a system that computes a frequency-domain transfer function between femoral and carotid pulse pressure signals and, using an electrical circuit-based model, derives aortic blood flow. This '828 patent does not teach or suggest any method for using the frequency-domain pulse pressure signals to compute arterial blood flow beneath the pressure sensor(s).
U.S. Pat. No. 5,048,533, METHOD AND APPARATUS FOR A NONINVASIVE EXAMINATION OF BLOOD CIRCULATION IN A LIVING ORGANISM, to Muz discloses a method in which two inflatable cuffs, each mounted around a different artery, are used to derive a real-time blood pressure signal.
U.S. Pat. No. 5,626,141, BLOOD PRESSURE MEASUREMENT APPARATUS AND ASSOCIATED METHOD, to Takeda describes a cuff-based device for measuring the velocity and acceleration of an underlying arterial wall.
U.S. Pat. No. 5,724,980, PULSE DIAGNOSIS METER, to Nakamura et al. discloses a device in which pulse signals from sensors on right-hand and left-hand fingers, are compared to detect abnormal differences in blood pressure between right and left sides of the body.
U.S. Pat. No. 5,743,857, BLOOD PRESSURE MONITOR APPARATUS, to Shinoda et al. discloses a device which monitors a phase difference between electrocardiographic signals, obtained from two different parts of the body, as a means for determining when to initiate a blood pressure measurement—thus avoiding unnecessary cuff inflations.
U.S. Pat. No. 5,724,981, PERIPHERAL ARTERIAL MONITORING INSTRUMENTS to Apple discloses a device for measuring arterial volume and compliance using an oscillometric approach, but with an improved cuff, capable of quantifying the amount of air expelled therefrom during the step-by-step deflation cycle. The '981 patent does not teach, or suggest, any technique for computing arterial wall lumen size or thickness.
U.S. Pat. No. 4,718,428, METHOD FOR DETERMINING DIASTOLIC ARTERIAL BLOOD PRESSURE IN A SUBJECT; U.S. Pat. No. 4,718,427, METHOD FOR DETERMINING SYSTOLIC ARTERIAL BLOOD PRESSURE IN A SUBJECT; U.S. Pat. No. 4,718,426, METHOD FOR DETERMINING DIASTOLIC ARTERIAL BLOOD PRESSURE IN A SUBJECT; and U.S. Pat. No. 4,669,485, APPARATUS AND METHOD FOR CONTINUOUS NONINVASIVE CARDIOVASCULAR MONITORING, all to Russell, disclose indirectly related prior-art approaches by the present inventor.
While the aforementioned patents teach a variety of useful system components—e.g., computerized sampling systems, FFT processors, cuff inflation/deflation apparatus, a volume-quantified pressure cuff, waveform displays, etc.—and each of said patents is HEREBY INCORPORATED BY REFERENCE for its teaching of elements/components useful in connection with the present invention, none of these patents disclose, or even remotely suggest, a practical, economical, accurate and non invasive method for monitoring blood flow.
Accordingly, there exists a long-felt, but unsatisfied, need for a reliable, economical and noninvasive technique for measuring arterial blood flow. There also exists a long-felt, but unsatisfied, need for a technique capable of providing such measurements on a continuous and/or real-time basis. There still further exists a long-felt, but unsatisfied, need for improved critical care and surgical monitoring techniques that incorporate continuous and/or real-time flow-related data. Finally, there exists a long-felt, but unsatisfied, need for improved techniques for diagnosing, monitoring, managing and/or treating patients with cardiovascular conditions and/or patients who are taking potentially vasoactive drugs or drug combinations. The present invention addresses these, as well as other, needs.